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<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
    // 找出下面23行的打印 a=10 是否有问题，如果有问题说出原因
    let a = 10;
    let b = 20;

    function fn1() {
      function fn2() {
        a = 200;
      }
      fn2()
    }

    console.log(a);  // 10
    fn1()
  </script>
</body>
</html>